Power circuit-breaker

ABSTRACT

A protective switching device, such as a differential-current circuit breaker, having a corebalance transformer which monitors a line network and which, via a tripping circuit and an actuation circuit, actuates a release which is coupled to a switching mechanism in order to operate a power breaker. The invention provides that a tripping circuit, which can be tripped by means of a remote tripping signal, is connected to a transformer which can be actuated on the secondary side and whose primary side is connected to an actuation circuit of the release for remote tripping of the protective switching device.

CLAIM FOR PRIORITY

This application claims priority to International Application No.PCT/DE99/01074 which was published in the German language on Oct. 28,1999.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a protective switching device, and inparticular to a differential-current circuit breaker, having acore-balance transformer which monitors a line network and which, via atripping circuit and an actuation circuit, actuates a release which iscoupled to a switching mechanism in order to operate a power breaker.

BACKGROUND OF THE INVENTION

Such a protective switching device is described in (U.S. Pat. No.4,001,646). The protective switching device is used to ensure protectionagainst a dangerous body current in an electrical system. For example,when someone touches a live part of an electrical system, the faultcurrent then flows via the person as a body current to ground. Thecircuit breaker which is used for protection against dangerous bodycurrents safely and rapidly isolates the relevant circuits from themains power supply when the so-called rated fault current is exceeded.

The construction of a circuit breaker is described, for example, from“etz”, Volume 107 (1986), issue 20, pages 938 to 945. There, FIGS. 1 to3 in particular show basic circuit diagrams and functional principles ofa fault-current circuit breaker (FI circuit breaker) and adifferential-current circuit breaker (DI circuit breaker).

FI and DI circuit breakers are constructed in a similar way from threeassemblies. A core-balance transformer, through whose transformer coreall the current-carrying conductors of a line network are passed inducesa voltage signal in its secondary winding in the event of a faultcurrent, and this voltage signal actuates a release which is connectedto the secondary winding. For its part, the release is coupled to aswitching mechanism via which, when the release is operated, thecontacts of a power breaker connected in that line or in each line areopened. In the process, the FI circuit breaker draws the energy requiredfor tripping from the fault current itself, irrespective of the mainspower supply voltage, while tripping in the case of a DI circuit breakertakes place as a function of the mains power supply voltage. To thisend, when a fault current occurs in the electrical circuit supplied fromthe line network, the signal emitted from the core-balance transformeris supplied, after amplification by means of an electronics unit that isdependent on auxiliary energy, to the DI tripping circuit of the DIcircuit breaker or DI accessory.

A test device having a test button is provided for checking theserviceability of such a protective switching device for circuitbreaker, which test button is normally connected between the neutralconductor (N) and a phase conductor (L1, L2, L3) of the line network.When the test button is pressed, a fault current is simulated, and thereaction of the circuit breaker is tested. In this case, the circuitbreaker must trip with virtually no delay when in the serviceable state.

Furthermore, a remote release is frequently provided in such circuitbreakers, via which—for example for disconnection—the circuit breakerand thus the power breaker coupled to it can be operated externally. Inorder to provide a remote release for a DI circuit breaker, one optionis for a mate contact to be connected in parallel with the test contactvia a remote tripping line connected to said DI circuit breaker. Anotheroption is for a separate winding to be provided in addition to the testwinding on the core-balance transformer. The separate winding isconnected between two external conductors or between one phase conductorand the neutral conductor via a current limiting resistor, for operationof a remote tripping switch. These two versions for remote tripping onthe one hand also require at least one auxiliary contact, however, in adisadvantageous manner. On the other hand, the feeders to the remotetripping switch and the switch contact for the remote release must bedesigned for a particularly high withstand voltage.

In the case of a DI accessory for power breakers, an additionalexacerbating factor is that no auxiliary contacts can be provided owingto the switching paths accommodated in the power breaker. Since suchcircuit breakers are also designed with three poles, a connectionbetween two outer conductors would also be required. Furthermore, aparticular feature of DI circuit breakers or accessories is thattripping time delays of up to one second can frequently be set. Thus, ifthe remote release were operated according to the said variance, arelatively long tripping time would have to be taken intoaccount—depending on the time delay setting. However, this isunacceptable with regard to emergency disconnection.

SUMMARY OF THE INVENTION

In one embodiment of the invention, there is a protective switchingdevice including a corebalance transformer which monitors a line networkand actuates a release which, via a tripping circuit and an actuationcircuit, is coupled to a switch mechanism in order to operate a powerbreaker, wherein a tripping circuit, which can be tripped by a remotetripping signal, is connected to a transformer which can be actuated onthe secondary side and whose primary side is connected to an actuationcircuit of the release.

In one aspect of the invention, if the secondary of the transformer isshort-circuited, the tripping circuit produces a control signal for theactuation circuit of the release.

In another aspect of the invention, the tripping circuit comprises anoscillator which is connected to the primary side of the transformer.

In yet another aspect of the invention, the oscillator is a square-wavegenerator whose frequency is set to between 500 Hz and 5 Hz.

In still another aspect of the invention, the protective switchingdevice wherein the tripping circuit has a comparator which is connectedon the primary side to the transformer and is connected on the outputside to the actuation circuit for the release.

In another aspect of the invention, the protective switching devicewherein the tripping circuit has a non-reactive resistor

RS>10 kΩ which is connected to the primary winding of the transformer.

In another aspect of the invention, the tripping circuit has a referencesignal source having a voltage divider which is fed from a supplyvoltage, via a zener diode.

In yet another aspect of the invention, a secondary of the transformeris connected to ground potential via a resistor series circuit.

In still another aspect of the invention, the actuation circuitcomprises a comparator with a downstream controllable electronic switch,which is connected to the release.

In yet another aspect of the invention, the controllable switch is atransistor whose base control input is connected to the comparator andin whose collector-emitter circuit a tripping relay coil of the releaseis connected.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will be explained in moredetail in the following text with reference to a drawing.

FIG. 1 shows the design of a DI circuit breaker with a tripping circuitfor remote tripping.

FIG. 2 shows the circuit design of the tripping circuit shown in FIG. 1.

Mutually corresponding parts are provided with the same referencesymbols in both figures.

DETAILED DESCRIPTION OF THE INVENTION

The invention discloses a protective switching device which can betripped remotely in a simpler and more reliable manner. The trippingcircuit comprises a transformer which has a primary winding and a secondwinding and whose primary is connected via an actuation circuit to therelease. When the transformer is actuated, circuiting its secondarywinding, produces a control signal for primary side of the transformer.

The tripping circuit expediently also has an oscillator in the form of asquare-wave generator, which acts on the primary winding of thetransformer. In order to keep the current drawn by the square-wavegenerator or oscillator as low as possible in this case, the frequency,on the one hand, is chosen to be as high as possible since the inductiveimpedance of the primary winding of the transformer increases inproportion to the frequency. Since, on the other hand, the remotetripping line which is connected to the transformer has an impedancewhich becomes increasingly low as the frequency increases owing to theparasitic capacitance between the conductor cores, the frequency isexpediently set to between 500 Hz and 5 kHz. The frequency levels areoptimized to the assumed primary inductance of the transformer of notless than 1 Henry, preferably by short the tripping circuit the releaseon the and to a cable length between the transformer and a remotetripping switch of not more than 300 m.

In one embodiment, the tripping circuit has a comparator which isconnected on the primary site to the transformer and is connected on theoutput side to the actuation circuit of the release. It is thus possibleto set a response threshold for the release for remote tripping bycomparing the signal on the primary side of the transformer with areference signal in order to produce an appropriate actuation signal.

In order to limit the current flow through the primary winding of thetransformer when a secondary winding is short-circuited, a non-reactiveresistor is connected downstream of the comparator within the trippingcircuit on the primary side of the transformer. This is particularlyadvantageous if the power supply for the tripping circuit is live afterremote tripping. A resistor of not less than 10 kg is particularlyexpedient with regard to a minimum current draw.

In one advantageous refinement, the reference signal source provided toproduce the reference signal within the tripping circuit has a referencevoltage divider which is connected in series with a zener diode to asupply voltage. This means that the reference voltage is zero for aslong as the rising operating voltage remains below the response voltageof the zener diode when the supply voltage is connected. As a result ofthe supply voltage being switched off, the reference voltage falls tozero when the falling operating voltage becomes less than the responsevoltage of the zener diode. This effectively prevents spurious trippingcaused by remote tripping electronics when the voltage supply is beingswitched on and off.

In order to prevent an electrostatic charge on the line which isconnected to the transformer for remote tripping, the secondary of thetransformer is expediently connected to ground potential by a series ofcircuits comprising at least two non-reactive resistors.

The actuation circuit preferably has a comparator which is connected onthe output side via a controllable electronic switch to the release. Theelectronic switch is expediently a transistor, whose control input isconnected to the comparator and in whose collector-emitter circuit thetripping relay coil of a tripping relay is connected.

The invention can achieve remote tripping without any auxiliary contactby a tripping circuit which acts on the release of a protectiveswitching device connected on the secondary side of a corebalancetransformer and has a transformer whose primary is connected to therelease. Furthermore, there is no need for any special requirements forthe withstand voltage of the remote tripping line and the remotetripping switch. Since the tripping circuit acts directly via theactuation circuit on the release, there is virtually no delay in theactuation for remote tripping of a circuit breaker with a tripping timedelay, so that safe emergency disconnection is ensured by remotetripping of the circuit breaker.

FIG. 1 shows the basic functional design of the differential-currentcircuit breaker as a protective switching device having a trippingcircuit 2 and having an actuation circuit 3, which is fed from thistripping circuit 2, for a release 4, as well as having a trippingcircuit 5 for remote tripping. The tripping circuit 2 comprises acore-balance transformer 6, through whose primary transformer core 7 allthe current-carrying lines of a single-phase or polyphase line networkLn are passed. The secondary winding 8 of the core-balance transformer 6is connected to a comparator 13 in the actuation circuit 3 via anelectronic amplifier 10 with rectification and with a tripping timedelay 12 connected downstream from it.

The comparator 13 is connected on the output side to a controllableelectronic switch which is connected to the release 4. In the exemplaryembodiment, the switch is a bipolar npn transistor 14, whose base isactuated by the comparator 13 and in whose collector-emitter circuit,which is connected to an operating voltage U_(B), a tripping releasecoil 15 of the release 4 is connected. The release 4 is coupled to amechanism in the form of a switching mechanism 16 which acts on aswitching path, connected in each line of the line network Ln, of apower breaker 18.

When the DI circuit breaker is operating in the absence of any faults,the vectorial sum of the currents flowing in the two directions in theline network is equal to zero. However, if a fault current via groundoccurs, for example as a result of an insulation fault in a load device(not illustrated), then this interferes with the current equilibrium inthe core-balance transformer 6. The transformer core 7 is magnetized ina corresponding way to the magnitude of the fault current, so that avoltage is induced in the secondary winding 8 of the core-balancetransformer 6. A corresponding amplified, rectified and a time-delaytripping signal S_(a), is supplied to the actuation circuit 3 of therelease 4. When the release 4 responds, the switching paths of the powerbreaker 18 are opened via the switching mechanism 16, and the damagedpart of the system is consequence disconnected.

The release 4 can furthermore be actuated by remote tripping. To thisend, the tripping circuit 5 comprises a transformer 20 having a primarywinding N1 and a secondary winding N2, via which the tripping circuit 5can be activated by means of a remote tripping signal S_(f). Asquare-wave oscillator 22 acts on the primary winding N1 of thetransformer 20. If the secondary of the transformer 20 isshort-circuited, then the voltage across the primary winding N1 of thetransformer 20 collapses. This is detected by a comparator 24 connectedon the primary side to the transformer 20. On exceeding a referencevoltage U_(Ref), the comparator 24 acts on the tripping circuit 2 toactuate the tripping relay coil 15 of the release 4, by the trippingcircuit 5 supplying the comparator 13 .of the actuation circuit 3 withan appropriate control signal S. In this case, this action takes placeafter the tripping circuit 2, and thus after the tripping time delay 12,if such a tripping time delay 12 is provided.

FIG. 2 shows the design of the tripping circuit 5 for remote tripping.The transformer 20 has a voltage divider which is connected in parallelwith the secondary winding N2 and is formed by two non-reactiveresistors R11 and R12 which are connected to ground PE. This preventsany electrostatic charge on the remote tripping line (not shown) whichis connected from the remote release to the connections FA1 and FA2.

The remote tripping lines are connected to the secondary winding N2 ofthe transformer 20 via connections FA1 and FA2. The square-waveoscillator 22 which is connected to the primary winding NI is formed bya comparator V1 with the illustrated circuitry comprising the resistorsR1 to R4 and the capacitor C1. The frequency f of the square-waveoscillator 22 is set by appropriate dimensioning of the time constantτ=R1×C1.

In order to keep the current drawn by the oscillator 22, and thus by thetripping circuit 5, as low as possible taking into account the impedance(X_(c)=½πfC), which decreases as the frequency f increases owing to theparasitic capacitance between the conductor cores of the remote trippinglines, and taking into account the inductive impedance (X_(L)=2πfL) ofthe primary winding N1, which increases with the frequency f, thefrequency f is preferably set to between 500 Hz and 5 kHz. This takesinto account a primary inductance L_(p)≧1H which can be achieved for aminimum physical volume of the transformer 20, and a cable length 1between the transformer 20 and a remote tripping switch (not shown) of1≦300m.

The voltage across the primary winding N1 of the transformer 20 isrectified and smoothed by means of a diode D1 and a capacitor C2. If thesecondary winding N2 of the transformer 20 is short-circuited as theresult of remote tripping,-then the voltage across the primary windingN1 collapses, and the capacitor C2 is discharged via a resistor R6connected in parallel with it. When the voltage across the capacitor C2becomes less than the reference voltage URef of the comparator 24, whichis designed as an inverting comparator V2 with hysteresis, then itsoutput changes from low level to high level. To this end, the comparatorV2 is connected to the resistors R9, R10 and to the capacitor C3 in themanner illustrated. The level change is used for controlling theactuation circuit 3 by the comparator V2 (24) supplying the appropriatecontrol signal S_(S) via the comparator 13 to the base control input ofthe transistor 14. This results in the transistor 14 being switched on,so that current flows through the tripping relay coil 15 of the release4, which is connected to the operating voltage U_(B) via thecollector-emitter circuit of this transistor 14. A resistor R5, which isconnected downstream on the output side of the comparator VI of thesquare-wave oscillator 22 and is located in the primary winding N1 ofthe transformer 20, limits the current flow via the primary winding N1when the secondary winding N2 is short-circuited in the situation wherethe power supply is live after remote tripping. In order to achieve aminimum current draw, R5 should be chosen to be≧10 kΩ.

The reference voltage URef of the comparator V2 is produced by means ofa reference voltage divider R7, R8, which is connected to a supplyvoltage UV and contains a series-connected zener diode D2. As long asthe rising operating voltage of the tripping circuit 5 is less than theresponse voltage of the zener diode D2 when the supply voltage U_(V) isconnected, the reference voltage is U_(Ref)=0 V. When the supply voltageU_(V) is disconnected, the reference voltage URef falls to 0 V when thefalling operating voltage of the tripping circuits falls below theresponse voltage of the zener diode D2. Spurious tripping caused byremote tripping electronics when the supply voltage U_(V) is beingswitched on and off is thus effectively prevented.

In an alternative method of operation of the DI circuit breaker, thesecondary of the transformer 20 is short-circuited using a break contactas a remote tripping switch. Undershooting of the reference voltageU_(Ref) would then result in actuation of the release 4 owing to achange in the control signal S_(S) of the comparator 24 (V2) in thetripping circuit 5.

What is claimed is:
 1. A protective switching device comprising: a corebalance transformer which monitors a line network and actuates a release which, via a tripping circuit and an actuation circuit, is coupled to a switch mechanism in order to operate a power breaker, wherein a tripping circuit, which can be tripped by a remote tripping signal, is connected to a transformer which can be actuated on the secondary side and whose primary side is connected to an actuation circuit of the release.
 2. The protective switching device claimed in claim 1, wherein, if the secondary of the transformer is short-circuited, the tripping circuit produces a control signal for the actuation circuit of the release.
 3. The protective switching device claimed in claim 1, wherein the tripping circuit comprises an oscillator which is connected to the primary side of the transformer.
 4. The protective switching device claimed in claim 3, wherein the oscillator is a square-wave generator whose frequency is set to between 500 Hz and 5 Hz.
 5. The protective switching device claimed in claim 1, wherein the tripping circuit has a comparator which is connected on the primary side to the transformer and is connected on the output side to the actuation circuit for the release.
 6. The protective switching device claimed in claim 1, wherein the tripping circuit has a non-reactive resistor RS≧10 kΩ which is connected to the primary winding of the transformer.
 7. The protective switching device claimed in claim 1, wherein the tripping circuit has a reference signal source having a voltage divider which is fed from a supply voltage, via a zener diode.
 8. The protective switching device claimed in claim 1, wherein a secondary of the transformer is connected to ground potential via a resistor series circuit.
 9. The protective switching device claimed in claim 1, wherein the actuation circuit comprises a comparator with a downstream controllable electronic switch, which is connected to the release.
 10. The protective switching device as claimed in claim 9, wherein the controllable switch is a transistor whose base control input is connected to the comparator and in whose collector-emitter circuit a tripping relay coil of the release is connected. 